Extruder transition section

ABSTRACT

A method and system are provided that efficiently compound high levels of inorganic filler, processing fluid and silicone polymer at a commercial rate into homogeneous filled and devolatilized silicone compositions. In the method, filled silicone compositions are compounded by compounding a filler, processing fluid and silicone polymer in a first compounding apparatus to produce a first dispersed composition and simultaneously compounding a filler, processing fluid and silicone polymer in a second compounding apparatus that shares a common extruder shaft with the first compounding apparatus to produce a second dispersed composition. The system comprises a first compounding apparatus and a sequential second compounding apparatus that shares a common shaft with the first compounding apparatus. An extruder transition section of the system includes an enclosed discharge chamber defined by a first sectioning wall, a second sectioning wall and a contoured lower wall that transitions toward a discharge port and a shaft extends through the first sectioning wall, traverses the chamber and extends through the second sectioning wall.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a sequential method and system tocompound heat-vulcanizable silicone compositions.

[0002] A heat-vulcanizable silicone composition comprises a highviscosity silicone polymer, an inorganic reinforcing filler and variousadditives that aid processing or impart desired final properties to thecomposition. A vulcanizing agent can be added and the compositionheat-cured to fabricate silicone rubber moldings such as gaskets,medical tubing and computer keypads.

[0003] Typically, the heat-vulcanizable silicone composition is producedby kneading a high-viscosity polydiorganosiloxane, the inorganic fillerand additives by means of a batch kneading machine such as a highintensity Banbury mixer or a low intensity double arm dough mixer. Inthis process, polydiorganosiloxane, inorganic filler and treating agentsare batch mixed until desired properties are obtained. This processrequires long residence times and large amounts of energy.Non-homogeneous shear and extensional stresses across a commercial sizedbatch can result in non-uniform size distribution of filler that resultsin variations in properties. Batches processed at different times may becharacterized by different physical properties. The batch process islabor, energy and capital intensive and produces materials of onlymarginal consistency.

[0004] In Kasahara et al., U.S. Pat. No. 5,198,171, a premix is formedin a first step wherein a polydiorganosiloxane having a viscosity at 25°C. of 1×10⁵cP or more, an inorganic filler and a treating agent aremixed in a high-speed mechanical shearing machine. The step produces aflowable particulate mixture in which each ingredient is present in asubstantially uniform, finely dispersed state. The premix is then fed ata constant feed rate into an extruder that has two screws rotating inthe same direction and has a length to diameter ratio (L/D) of 25 to 50.

[0005] In Hamada et al., U.S. Pat. No. 5,409,978, a premix ofpolydiorganosiloxane, inorganic filler and treating agents is formed ata temperature in the range of about 200° C. to 300° C. in a co-rotatingcontinuous double screw extruder with L/D of about 25 to 50. The premixis then compounded and heat treated at 150° C. to 300° C. in acounter-rotating, double screw extruder. A useful L/D ratio for thesecond extruder is in the range of about 5 to 15.

[0006] Highly vigorous first step processes for forming a premix ofsilicone polymer, filler and treating agent generate a product having ahigh volatiles content. The premix must be mixed with additional polymerand devolatilized in a second step to produce a useful product. Othernewer processes that avoid a premix and/or that use a raw untreatedfiller can be limited in throughput. Larger diameter extruders willincrease throughput. However, larger diameter extruders must be custombuilt. Hence, larger extruders are expensive and cost more per unitcapacity. There is a need for a process that continuously andconsistently produces a devolatilized high viscosity filled siliconepolymer composition at high throughput. Further, there is a need for animproved continuous compounding method that efficiently utilizescompounding equipment while providing commercial scale production.

BRIEF SUMMARY OF THE INVENTION

[0007] The invention provides a method and system that efficientlycompounds high levels of inorganic filler, processing fluid and siliconepolymer at a commercial rate into homogeneous filled and devolatilizedsilicone compositions. In the method, filled silicone compositions arecompounded by compounding a filler, processing fluid and siliconepolymer in a first compounding apparatus to produce a first dispersedcomposition. Simultaneously, filler, processing fluid and siliconepolymer are compounded in a second compounding apparatus that shares acommon extruder shaft with the first compounding apparatus to produce asecond dispersed composition.

[0008] The system comprises a first compounding apparatus and a secondcompounding apparatus that shares a common shaft with the firstcompounding apparatus.

[0009] In another embodiment, the invention relates to an extrudertransition section. The section comprises an enclosed discharge chamberdefined by a first sectioning wall, a second sectioning wall and acontoured lower wall that transitions toward a discharge port. A shaftextends through the first sectioning wall, traverses the chamber andextends through the second sectioning wall.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a schematic representation of a silicone compositioncompounding process and system; and

[0011]FIG. 2 is a schematic representation of a transition section usedwith the process and system of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0012] A process and system are provided by the invention to compoundhigh levels of components such as treated or untreated fumed silica andprocessing fluid into a silicone polymer, such as high molecular weightpoly(dimethylsiloxane). The process and system produce homogeneousmixtures having required reinforcing properties and levels of residualvolatiles at satisfactory commercial throughputs. The process includesat least two sequential compounding steps, wherein filler and siliconepolymer are mixed and compounded.

[0013] The processing fluid is a fluid that can be admixed with a fillerand compounded to densify the filler for further processing. Theprocessing fluid can also provide a processing function. For example, itcan be a liquid treating agent, plasticizer, flow improving additive,cross-linking agent, water or inert blanketing gas. Silicone polymers ofa molecular weight greater than 7000 are not processing fluids.Preferably, the processing fluid is a liquid treating agent such as asilanol-reacting treating agent that can be added before, with or afteraddition of filler to wet the filler to reduce overall processing timefor reaction between functional groups in the treating agent andsilanols on the surface of the filler.

[0014] In one embodiment, the processing fluid is a solution prepared bymixing (in weight) 1.21 parts of a silanol-stopped polydimethylsiloxane,1.82 parts of a vinyl-stopped dimethyl-methylvinylsiloxane and 0.12 partof a hydroxy-terminated polydimethyl-methylvinylsiloxane. A broad rangeof parts of silanol-stopped polydimethylsiloxane/vinyl-stoppeddimethyl-methylvinylsiloxane/hydroxy-terminatedpolydimethyl-methylvinylsiloxane can be 0.49/0.73/0.05 to1.93/2.91/0.19, a desired range is 0.85/1.27/0.08 to 1.57/2.37/0.16 anda preferred range is 1.09/1.64/0.11 to 1.32/2.0/0.13

[0015] In another embodiment, the processing fluid can be a combinationof treating agent, preferably hexamethyldisilazane (HMDZ) and water.This combination can comprise a weight ratio of treating agent/water ofbetween about 0.05 to about 50, preferably between about 0.1 and about20, and more preferably between about 1 and about 6. The HMDZ can beadded either together with water or separately at the same or differentlocations of an extruder.

[0016] The processing fluid can be combined with filler in a weightproportion of about 0.1 to about 100 parts fluid to 100 parts of filler,desirably about 0.5 to about 75 parts fluid to 100 parts of filler andpreferably about 1.0 to about 50 parts fluid to 100 parts of filler. Theprocessing fluid can be added at a single location or at a plurality oflocations of the compounding apparatus for step treatment of the filler.

[0017] The inorganic filler can be any inorganic filler used in blendswith silicone polymers. Examples of inorganic fillers include areinforcing silica such as fumed silica or precipitated silica or asilica that has been surface-treated with an organosilicon compound suchas an organopolysiloxane, organoalkoxysilane, organochlorosilane or ahexaorganodisilazane. The filler can be diatomaceous earth, finelycrushed quartz, aluminum oxide, titanium oxide, iron oxide, ceriumoxide, cerium hydroxide, magnesium oxide, zinc oxide, calcium carbonate,zirconium silicate, carbon black or ultramarine. A single filler or acombination of fillers can be used to reinforce the silicone polymer.

[0018] The amount of the filler can be in the range of from about 5 toabout 200 parts by weight, desirably from about 10 to about 100 parts byweight and preferably from about 20 to about 60 parts by weight, per 100parts by weight of silicone polymer.

[0019] The concentration of residual silanol groups on the surface of afiller can govern strength of hydrogen bonds between the silica andhydroxyl or oxygen groups in the silicone polymer chain. Highconcentrations of residual silanols in a filler cause “structuring” or“crepe hardening” of the final product in storage. This effect leads todifficulties in the processing of the material after it has been storedfor extended periods. If the concentration of silanol functional groupsin a filler is too high, a treating agent can be added to reduce thegroups to a required concentration. The silanol reactant treating agentcan react to reduce available groups to a concentration of between about8 to about 2 hydroxyl groups/(nanometer)² of filler, preferably betweenabout 5 to about 3 hydroxyl groups/(nanometer)² of filler. Untreated rawsilica is a preferred filler in the invention, in an amount from about10 to about 100 parts by weight, preferably from about 20 to about 60parts by weight, per 100 parts by weight of silicone polymer.

[0020] A treating agent can be mixed into the filler along with theprocessing fluid or the treating agent can be the processing fluid toreduce filler silanol groups and/or to improve dispensability of thefiller to prevent crepe hardening and/or to regulate plasticity. Thetreating agent can be the silanol-reacting reagent or another fillertreating agent. The treating agent is preferably a silanol reactanttreating agent when the filler is a silica or other silanol containingfiller. The treating agent can be an organosilane, a low-viscositypolysiloxane or a silicone resin, which has a silanol group and/or analkoxy group having 1 to 6 carbon atoms. Examples includediphenylsilanediol, dimethylsilanediol, methyltriethoxysilane andphenyltrimethoxysilane. The low-viscosity polysiloxane may contain oneor more kinds of organic groups selected from a methyl group, a phenylgroup, a vinyl group and a 3,3,3-trifluoropropyl group. The viscosity ofthe low-viscosity polysiloxane measured at 25° C. is in the range offrom about 1 to about 300 cP, preferably from about 5 to about 100 cP.Preferred silanol-reactant treating agents include at least one ofsilanol-stopped polydimethylsiloxane, octamethylcyclotetrasiloxane (D4)and hexamethyldisilazane (HMDZ). While the filler can be treated asdescribed, a particular advantage is that raw untreated filler can beused in the inventive process.

[0021] The silicone polymer used in the compositions of the presentinvention is represented by recurring units of Formula I:

[0022] wherein, R¹ independently at each occurrence represents C₁₋₄alkyl, or C₂₋₄ alkylene; R² independently at each occurrence representsC₁₋₄ alkyl, C₁-C₄ haloalkyl or C₂₋₄ alkylene; R³ independently at eachoccurrence represents H, C₁₋₁₀ alkyl, C₂₋₄ alkylene, C₄₋₆ cycloalkyl, OHor C₁-C₄ haloalkyl; and n represents an integer from about 100 to about20,000.

[0023] A further preferred composition comprises a silicone polymerwherein, R¹ independently at each occurrence represents, CH₃ or CH═CH₂;R² independently at each occurrence represents, CH₃, CH═CH₂ orCH₂CH₂CF₃; R³ independently at each occurrence represents CH₃, CH═CH₂,OH or CH₂CH₂CF₃; and n represents an integer from about 4,000 to about10,000.

[0024] In one embodiment, the vinyl content of the silicone polymerranges from about 0.05% to about 0.5% by weight of the silicone polymer.

[0025] The silicone composition can also include other additives such asheat-resistance improvers such as oxides, hydroxides and fatty acidsalts of metals, vulcanization reverse inhibitors, flame retardants suchas platinum compounds, discoloration preventive agents, plasticizerssuch as silicone oil, internal release agents such as metal soaps,pigments and dyes.

[0026] During processing, an inert blanketing gas can be added to thecompounding environment to suppress oxidative reactions between aflammable processing fluid such as HMDZ, and air. The amount of inertgas can be in the range of from about 20 to about 800 parts by weight,desirably from about 50 to about 600 parts by weight and preferably fromabout 100 to about 400 parts by weight per 100 parts by weight of thefiller.

[0027] In an embodiment of the invention, untreated fumed silica fillercan be mixed with a processing fluid that comprises HMDZ and water at afirst location prior to addition of the silicone polymer. The amount ofHMDZ can be in the range of from about 0.1 to about 100 parts by weight,desirably from about 0.5 to about 50 parts by weight and preferably fromabout 1.0 to about 20 parts by weight, per 100 parts by weight of thefumed silica. The amount of water can be in the range of from about 0.1to about 100 parts by weight, desirably from about 0.5 to about 20 partsby weight and preferably from about 1 to about 10 parts by weight, per100 parts by weight of the fumed silica.

[0028] The compositions produced by the process of the invention meetphysical property standards for heat-vulcanizable silicone compositions.For example, the compositions can be characterized by a WilliamsPlasticity greater than 100, Shore A hardness greater than 20, tensilestrength greater than 750 psi, elongation at break at least 100%, Tear Bat least 10 ppi, Specific Gravity at least 1.05 and residual volatilesbelow 1 weight percent.

[0029] Features of the invention will become apparent from the followingdrawings and detailed discussion, which by way of example withoutlimitation describe embodiments of the present invention.

[0030] In the drawings, FIG. 1 is a schematic representation of asilicone composition compounding process and system and FIG. 2 is aschematic representation of a transition section used with the processand system of FIG. 1. In the FIGs., like elements are identified by thesame numbers.

[0031] In FIG. 1, a system 10 for compounding filled siliconecompositions is shown, comprising a first upstream compounding apparatus12 and a sequential second downstream compounding apparatus 14. Upstreamapparatus 12 and downstream apparatus 14 are shown contiguous to oneanother. The compounding apparatus 12 and 14 share common shaft 16,which drives extruder elements as hereinafter described.

[0032] Each compounding apparatus 12 and 14 can be a double screwapparatus of the co-rotating, intermeshing type, a counter-rotating,non-intermeshing type, a single-screw reciprocating or a single screwnon-reciprocating type. The co-rotating, intermeshing double screwapparatus is especially suited for the process of this invention due toits capability to provide adequate mixing intensity and surface arearenewal for filler dispersal, chemical reaction and devolatilization.

[0033] Further referring to FIGS. 1 and 2, the system 10 includes atransition section 18 that includes an enclosed discharge chamber 20that has a contoured lower wall 22 that transitions toward dischargeport 24. Shaft 16 is shown extending from the interior of upstreamapparatus 12 through first sectioning wall 26, traversing the transitionsection 18 and extending through second sectioning wall 28 into theinterior of downstream apparatus 14. Similarly, shaft 30 extends throughfirst section wall 26 to traverse the transition section 18 and toextend through second sectioning wall 28 into downstream apparatus 14.The shafts 16 and 30 are in the same horizontal plane but fordescription purposes are shown above one another in FIG. 1.

[0034] According to the invention, and as shown in the FIGS. 1 and 2,the shafts 16 and 30 are common to both upstream apparatus 12 anddownstream apparatus 14. The shafts 16 and 30 are shown commonly drivenby motor drive 32, however in other embodiments, the shafts 16 and 30are separately driven. The shafts 16 and 30 are shown having variouscompounding elements that make up a conveying stage 34, a kneading stage36 for distributive and dispersive mixing, churning stage 38 fordeairation and devolatilization and a discharge conveying stage 40.

[0035] Each of the upstream compounding apparatus 12 and the downstreamcompounding apparatus 14 has feed port 42 for charging raw untreated ortreated fumed silica, feed port 44 for charging a silanol treating agentsuch as HMDZ, feed port 46 for charging deionized water, feed port 48for charging a processing fluid and feed port 50 for charging a highmolecular weight silicone polymer. Each of the upstream compoundingapparatus 12 and the downstream compounding apparatus 14 has atmosphericvent 52, vacuum drawoff 54 and line 56 for charging an inert gas to thevacuum drawoff.

[0036] Downstream compounding apparatus 14 has discharge end 58 fordischarging highly filled elastomeric product. Product from the upstreamcompounding apparatus is conveyed out of the apparatus 12 and intotransition section 18. Particularly referring to FIG. 2, the transitionsection 18 includes discharge chamber 20 having a lower wall 22 thatslopes toward discharge port 24 as described above. Within thetransition section 18, shafts 16 and 30 include special screw tipelement 60 and spacer elements 62, shaft supporting bearings 64, shaftseal packing 66 and profile strand extrusion die 68. The transitionsection can be disconnectable to permit the first compounding apparatus12 to be disconnected from the second compounding apparatus 14.

[0037] In the method of FIGS. 1 and 2, filler, treating agent, deionizedwater, processing fluid, and silicone polymer are continuously suppliedfrom respective storage tanks 70, 72, 74, 76, and 78 into respectiveapparatus 12 and 14. In the apparatus 12 and 14, the filler, treatingagent, water, processing fluid and silicone polymer are continuouslycompounded and discharged at 24 and 58 as extrudates. The material inboth apparatus, 12 and 14, is compounded by elements on common shafts 16and 30, which are driven by motor 32.

[0038] Throughput and screw speed can be adjusted in the apparatus toallow for efficient compounding and devolatilization. Low throughputunderutilizes the capacity of manufacturing equipment. On the otherhand, throughput is limited by the rate at which fumed silica can beadded into an extruder. High screw speeds are needed for addition anddispersion of filler and dispersion of additives into the siliconematrix and for generation of surface area for devolatilization. However,temperature rises due to viscosity and screw speed. The use of severescrew speeds can result in thermal degradation of the silicone polymer.In the invention, scalable throughput with balanced mixing intensityprovides effective compounding and reaction of silicone compositioncomponents with adequate process devolatilization and heat dissipation.The sequential, contiguous arrangement permits operation at standardscrew conditions but with double throughput.

[0039] An extruder screw speed for apparatus 12 and 14, can be betweenabout 100 rpm and about 1000 rpm to provide a suitable balancing ofmixing with frictional heat generation. Desirably, the screw speed isbetween about 200 rpm and about 800 rpm and preferably between about 280rpm and about 450 rpm. A ratio of throughput to screw speed(lb/hour/rpm) can be between about 0.01 to about 100, desirably between0.1 and about 70 and preferably between about 0.5 and about 50lb/hour/rpm. Exterior barrel temperature for both apparatus 12 and 14,can be between about 100° C. and about 200° C., desirably between about130° C. and about 190° C., and preferably between about 160° C. andabout 180° C.

[0040] These and other features will become apparent from the followingexamples, which describe preferred embodiments of the present invention.

EXAMPLE

[0041] The following Example is conducted in the dual apparatus 10 ofFIG. 1. In FIG. 1, the upstream compounding apparatus 12 (designatedApparatus A) and downstream compounding apparatus 14 (DesignatedApparatus B) are commonly driven by shafts 16 and 30, which are drivenby motor drive 32. Both upstream compounding apparatus 12 and downstreamapparatus 14 have co-rotating, intermeshing double screw configurations(L/D=30, screw diameter=30mm). The apparatus 12 and 14 are joined bytransition section 18. While the combined length to diameter ratio (L/Dratio) of apparatus 12 and 14 is about 60, in other embodiments, thecombined L/D ratio can be greater than about 40 or even greater thanabout 60.

[0042] Fumed silica is simultaneously metered at 42 into apparatus 12and the downstream apparatus 14 along with treating agent at 44 anddeionized water at 46. Processing fluid is added at 48 and siliconepolymer is added at 50 into both apparatus. The processing fluid is acombination of a silanol-stopped polydimethylsiloxane, a vinyl-stoppeddimethyl-methylvinylsiloxane and a hydroxy-terminatedpolydimethyl-methylvinylsiloxane. Air entrained in the fumed silica andsurplus volatiles are eliminated through vents 52 and 54 in bothapparatus 12, 14.

[0043] Fumed silica-filled silicone compositions at a throughput ofabout 9 lb/hr of silicone polymer per apparatus are compounded in withabout 0.6 lb/hr HMDZ, 0.1 lb/h water, 1.0 lb/hr processing fluid, 4.7lb/hr untreated filler per apparatus at barrel temperatures of about170° C. and torque of 33%. TABLE 1 shows material properties for productfrom both Apparatus A and Apparatus B with common shaft according to theinvention. TABLE 1 Apparatus A Apparatus B Residual Voatiles (%) 0.3 0.4Shore A Hardness 66 64 Tensile Strength (psi) 1440 1460 Elongation atBreak (%) 390 440 Tear B (ppi) 135 140 100% Modulus 370 350 SpecificGravity 1.18 1.18 Williams Plasticity (10 minutes) 330 280 WilliamsPlasticity (3 weeks) 510 390 Transparency 78 78 Haze 21 23 YellownessIndex 12 13

[0044] The results of TABLE 1 show that the process of the invention canproduce materials within physical property standards for filledheat-vulcanizable silicone compositions.

[0045] The invention has been described in detail with particularreference to preferred embodiments thereof, but it will be understoodthat variations and modification can be effected within the scope of theinvention.

What is claimed is:
 1. A method of compounding a filled siliconecomposition, comprising: compounding a filler, processing fluid andsilicone polymer in a first compounding apparatus to produce a firstdispersed composition; and simultaneously compounding a filler,processing fluid and silicone polymer in a second compounding apparatusthat shares a common extruder shaft with said first compoundingapparatus to produce a second dispersed composition.
 2. The method ofclaim 1, wherein said second compounding apparatus is sequential to saidfirst compounding apparatus.
 3. The method of claim 1, wherein saidsecond compounding apparatus is sequential to and contiguous with saidfirst compounding apparatus.
 4. The method of claim 1, wherein saidsecond compounding apparatus is sequential to and contiguous with saidfirst compounding apparatus separated only by a transition section. 5.The method of claim 4, comprising discharging said first dispersedcomposition from said transition section.
 6. The method of claim 4,wherein said transition section, comprises an enclosed discharge chamberdefined by a first sectioning wall, a second sectioning wall and acontoured lower wall that transitions toward a discharge port and ashaft that extends through said first sectioning wall, traverses saidchamber and extends through said second sectioning wall.
 7. The methodof claim 6, wherein said shaft is common to said first compoundingapparatus and to said second compounding apparatus.
 8. The method ofclaim 7, further comprising disconnectable couplings that permit saidfirst compounding apparatus to be disconnected from said secondcompounding apparatus.
 9. The method of claim 1, wherein said commonextruder shaft is operated at a torque at least 60% of capacity toproduce dispersed compositions from both first and second compoundingapparatus.
 10. The method of claim 1, wherein said filler is a raw,untreated silica.
 11. The method of claim 1, wherein said filler is apretreated filler said pretreated filler being prepared by treatment ofan untreated filler with a filler treatment agent prior to beingcompounded.
 12. The method of claim 1, wherein said processing fluid isa silanol-reacting treating agent.
 13. The method of claim 1, whereinsaid filler contains silanol groups and said processing fluid is atreating agent comprising at least one of silanol-stoppedpolydimethylsiloxane, octamethylcyclotetrasiloxane orhexamethyldisilazane.
 14. The method of claim 1, wherein said processingfluid is selected from the group consisting of silanol-stoppedpolydimethylsiloxane, vinyl-stopped dimethyl-methylvinylsiloxane andhydroxy-terminated polydimethyl-methylvinylsiloxane
 15. The method ofclaim 1, comprising controlling said compounding to provide a totalthroughput to screw speed ratio in each said compounding apparatusbetween about 0.01 and about 100 lb/hour/rpm.
 16. The method of claim 1,comprising controlling said compounding to provide a total throughput toscrew speed ratio in each said compounding apparatus between about 0.1and about 70 lb/hour/rpm.
 17. The method of claim 1, comprisingcontrolling each said compounding to provide a total throughput to screwspeed ratio in each said compounding apparatus between about 0.5 andabout 50 lb/hour/rpm.
 18. The method of claim 1, wherein the compoundingis carried out under an inert gas.
 19. A method of compounding a filledsilicone composition, comprising: forming a premix of filler andsilicone polymer in a first mixer; compounding a portion of said premixwith additional silicone polymer in a first compounding apparatus toproduce a first dispersed composition; and simultaneously compounding atleast another portion of said premix and silicone polymer in a secondcompounding apparatus that shares a common extruder shaft with saidfirst compounding apparatus to produce a second dispersed composition.20. A system for compounding filled silicone compositions, comprising: afirst compounding apparatus; and a sequential second compoundingapparatus that shares a common shaft with said first compoundingapparatus.
 21. The system of claim 20, wherein said sequential secondcompounding apparatus is contiguous to said first compounding apparatus.22. The system of claim 20, wherein said sequential second compoundingapparatus is sequential to and contiguous with said first compoundingapparatus.
 23. The system of claim 20, wherein said first and secondcompounding apparatus are characterized by a combined L/D ratio ofgreater than
 40. 24. The system of claim 20, wherein said first andsecond compounding apparatus are characterized by a combined L/D ratioof greater than about
 60. 25. The system of claim 20, comprising aco-rotating, intermeshing double screw compounding apparatus.
 26. Thesystem of claim 20, comprising a counter-rotating, non-intermeshingdouble screw apparatus.
 27. The system of claim 20, comprising a singlescrew reciprocating apparatus.
 28. The system of claim 20, comprising asingle screw non-reciprocating apparatus.
 29. An extruder transitionsection, comprising an enclosed discharge chamber defined by a firstsectioning wall, a second sectioning wall and a contoured lower wallthat transitions toward a discharge port and a shaft that extendsthrough said first sectioning wall, traverses said chamber and extendsthrough said second sectioning wall.
 30. The extruder transition sectionof claim 29, wherein said section connects a first compounding apparatusto a second compounding apparatus.
 31. The extruder transition sectionof claim 30, wherein said shaft is common to said first compoundingapparatus and to said second compounding apparatus.
 32. The extrudertransition section of claim 31, further comprising disconnectablecouplings that permit said first compounding apparatus to bedisconnected from said second compounding apparatus.